Shannon Schroeder, 37, of Poulsbo, Wash., has a defibrillator monitoring her heartbeat and waiting for a chance to shock her back to life.

Though she rarely notices it's there, a few years ago, the defibrillator fired accidentally while Schroeder was taking her daughter to preschool and carrying her one-year-old.

Women are less likely to get ICDs, even though they are just as effective as they are in men.

"I felt this boom, like an energy wave, and looked around thinking there had been an earthquake. But no one else seemed to notice," she says. "Afterwards everything seemed so quiet and surreal." Fortunately she never lost her grip on her baby.

An implantable cardioverter defibrillator (ICD) is a little smaller than an iPod, but it packs a huge kick. If the thin wires running to the chambers of the heart detect ventricular fibrillationan often lethal arrhythmiathe ICD will unleash a burst of electricity to force the heart back into rhythm. It's similar to the heart paddles that television doctors use while yelling "Clear!" Except it never leaves your body. The experience of having the deviceand having it go offcauses anxiety, fear, and even depression in some .

A recent study found that implantable defibrillators can misfire in about 15% of patients. There's no doubt ICDs can save livesespecially for people whose hearts have been severely weakened by heart failure or a heart attackbut according to one estimate, only about 35% of Americans who are eligible for the device actually have them, even though insurance generally covers the cost. Women in danger of ventricular fibrillation are about 40% as likely as white men to get the devices, even though the device is equally effective for both sexes.

Adrian Hernandez, MD, a cardiologist at the Duke Clinical Research Institute, believes more patients with weakened heartsand especially more womenshould press the case for an ICD. "Patients need to be their own health advocates," Dr. Hernandez says.

But there's always a chance that the device could go off unnecessarily. In one recent study, about 15% of patients taking beta-blockers received inappropriate shocks each year. (Adding the anti-arrhythmia drug amiodarone to the treatment cut the occurrence to less than 5%.)